Hinge Mechanism and Vehicle Seat Comprising Such a Mechanism, and Method for Making Such a Mechanism

ABSTRACT

A hinge mechanism ( 6 ) for a vehicle seat, comprising: first and second frames mounted so that they can rotate relative to one another; and an annular ring comprising a cylindrical base which covers the peripheral edges of the frames, and first and second side flaps. The ring does not comprise a portion that is in contact with one of the inner faces of the frames.

The invention relates to hinge mechanisms, vehicle seats comprising suchmechanisms, as well as a method for making such mechanisms.

More specifically, the invention relates to a hinge mechanism for avehicle seat, comprising:

-   first and second frames mounted so that they can rotate relative to    one another about an axis, said frames comprising inner faces    oriented inward and facing one another, outer faces oriented outward    and away from each other, and circular peripheral edges distanced    from the axis, and-   an annular ring comprising a base which covers the peripheral edges    of the frames, and first and second side flaps which cover at least    a portion of each of the outer faces.

Document FR-A-2 915 436 describes an example of a hinge mechanism ofthis type, which has been satisfactory and in which the ringadditionally comprises a shoulder pressing on the inner face of thesecond frame. This allows shaping the second flap by crimping it betweenthe inner face and the outer face of the second frame. Due to thisshoulder of the ring and this crimping process, the first frame is notheld by the crimping of the first flap of the ring, which would preventthe first frame from rotating relative to the second frame. Operatingclearances are maintained between the first frame and the ring, thenbetween the second frame and the first frame, which allows the rotationto occur.

The goal of the invention is to propose an alternative assembly of thefirst and second frames which must be rotatable relative to each other.

For this purpose, the hinge mechanism of the above type is characterizedby the base having a cylindrical shape which extends in the direction ofthe axis directly between the first side flap and the second side flap,and by the ring not comprising a portion in contact with one of theinner faces of the frames.

Because of these arrangements, the ring is simpler in form whilepreserving the rotatability of the first and second frames relative toone another. The second frame does not have a radial extension againstwhich a shoulder of the ring presses. The second frame has an outsidediameter that is less than that of the prior art, and the hingemechanism of the invention is therefore less bulky.

Also, the second frame requires less material. It is therefore lesscostly.

In various embodiments of the hinge mechanism according to theinvention, one or more of the following arrangements may be applied.

In one aspect of the invention, axial play along the direction of theaxis is preserved between the first side flap and the first frame duringthe formation of the second side flap against the second frame.

In one aspect of the invention, the second frame has a diameter greaterthan a diameter of the first frame, and the difference between saiddiameters is less than 1 mm.

In one aspect of the invention, the second frame has a diameter equal toa diameter of the first frame.

In one aspect of the invention, the peripheral edge of the second frameis in close contact with an inner face of the base in order to attachthe ring solidly to the second frame.

In one aspect of the invention, the peripheral edge of the second framecomprises teeth which engage with the inner face of the base in order toattach the ring solidly to the second frame.

In one aspect of the invention, the first side flap comprisesindentations extending from said first side flap in the direction of theouter face of the first frame, said indentations being greater than orequal to three in number.

In one aspect of the invention, the base of the ring comprises a conicalinner face in order to grip the peripheral edge of the second frameradially and leave the peripheral edge of the first frame free torotate.

The invention also relates to a seat of a vehicle, comprising first andsecond parts connected to each other by a hinge mechanism as definedabove, the first frame being attached to the first part and the secondframe being attached to the second part.

In one possible arrangement, the first part is a frame of a seat backand the second part is a frame of a seat bottom.

The invention also relates to a method for making a hinge mechanism fora vehicle seat, comprising the following steps:

-   a) an assembly is provided which comprises:-   first and second frames able to be mounted so that they can rotate    relative to one another about an axis, said frames comprising inner    faces oriented inward and towards one another, outer faces oriented    outward and away from each other, and circular peripheral edges    distanced from the axis, and-   an annular ring comprising a cylindrical base which covers the    peripheral edges of the frames, and a first side flap which covers    at least a portion of the outer face of the first frame,-   b) a second side flap is formed by folding a portion of the ring    towards the outer face of the second frame and by pressing against    the outer face of the first frame.

By these arrangements, the ring is crimped onto the outer face of thesecond frame, forming a second flap. Simultaneously, an operatingclearance is preserved between the first side flap and the first frame.The hinge mechanism made in this manner preserves a second frame thatcan rotate relative to the first frame.

The ring is simpler in shape than the known rings which have a shoulderpressing on an inner face of the second frame.

In some embodiments of the method for making a hinge mechanism accordingto the invention, one or more of the following arrangements may be used.

In one aspect of the invention, the following step is carried outbetween steps a) and b):

-   the ring is positioned relative to the first frame with a    predetermined clearance with a first tool comprising first and    second surfaces, the first surface being adapted to press against    the first side flap, the second surface being adapted to press    against the first outer surface, and said surfaces being offset in    the direction of the axis to ensure said predetermined clearance    between an inner surface of the first side flap and the first outer    surface of the first frame, the ring being pushed towards said first    tool and said first tool being pushed towards said first frame so    that said surfaces are pressing against one another.

In one aspect of the invention, the ring is squeezed radially inwardonto the peripheral edge of the second frame.

In one aspect of the invention, step b) is carried out in at least thetwo following sub-steps:

-   b1) the portion of the ring is folded to a first angle to form a    flange sloping at said first angle, and-   b2) said flange is folded to a second angle, substantially 90°, to    form the second side flap facing the outer face of the second frame,    the assembly being pushed towards a die by a first tool pressing    against the outer face of the first frame.

In one aspect of the invention, the first angle is between 30° and 60°,and preferably substantially equal to 45°.

Other features and advantages of the invention will be apparent fromreading the following description of one of its embodiments provided asa non-limiting example, with reference to the attached drawings.

In the drawings:

FIG. 1 is a schematic view of a vehicle seat equipped with a hingemechanism according to an embodiment of the invention;

FIG. 2 is an axial cross-sectional view of a hinge mechanism accordingto the prior art;

FIG. 3 is an axial cross-sectional view of a hinge mechanism accordingto the invention;

FIG. 4 is an axial cross-sectional view of an enlarged portion of FIG.3;

FIG. 5 is an exploded perspective view of the hinge mechanism of FIG. 3;

FIG. 5 a is an enlarged view of a portion of the outer edge of thesecond frame shown in the exploded view of FIG. 5; and

FIGS. 6 a to 6 h are views showing successive steps of an embodiment ofa method for making the hinge mechanism according to the invention ofFIG. 3.

The same references are used to denote identical or similar elements inthe various figures.

FIG. 1 represents a front seat 1 of an automotive vehicle, whichcomprises a seat back 2 assembled to pivot about an axis Y1 on a seatbottom 3, said seat bottom being mounted onto a floor 4 of the vehicle,for example by means of slide rails 5.

The tilt of the seat back 2 is thus adjustable by means of a controllevel 6 a or similar device which drives a geared hinge mechanism 6 (amechanism which allows adjusting the tilt of the seat back 2).

This hinge mechanism 6 comprises (see FIG. 2 of the prior art and FIG. 3of the invention):

-   a first frame 7 formed by a first metal plate extending within a    plane perpendicular to the axis Y1 and which, in the example    represented, is solidly attached to the frame of the seat back 2,-   a second frame 8 formed by a second metal plate extending parallel    to the first frame 7, said second frame 8 being solidly attached to    the frame of the seat bottom 3, the first frame 7 being mounted so    that it can rotate relative to the second frame, and-   engaging elements which connect the first frame 7 to the second    frame 8, for adjusting the angular position between said frames (the    tilt of the seat back 2), and-   at least one input device, such as the control handle 6 a, for    controlling the setting of said angular position.

The first and second frames 7, 8 are held together at the outer edge ofthe hinge mechanism, by a ring 9.

The first and second frames 7, 8 and the ring 9 form a closed casingwhich delimits an inside and an outside. The engaging elements are onthe inside. The seat back 2 and the seat bottom 3 are on the outside.The elements of the hinge mechanism 6 will be advantageously definedwith these standard concepts of inside and outside relative to thisclosed hinge mechanism 6 assembly.

The first and second frames 7, 8 respectively comprise:

-   inner faces 71, 81 oriented towards the inside of the hinge    mechanism, meaning facing one another and close enough to come into    contact with each other on at least a peripheral portion of the    mechanism,-   outer faces 72, 82 oriented towards the outside of the hinge    mechanism, meaning facing away from each other, and-   circular peripheral edges 73, 83 located at the radial extremity of    the frames, distanced from the axis Y1.

The ring 9 is annular, of a general U shape with its opening facinginwards (towards the axis Y1).

In the embodiment known from the prior art, represented in FIG. 2 andsummarized in said document FR-A-2 915 436, the peripheral edge 83 ofthe second frame 8 has a diameter greater than the diameter of theperipheral edge 73 of the first frame. The second frame 8 thus comprisesan extension 85 in a radial direction perpendicular to the axis Y1,which forms a portion where the ring 9 is crimped onto each of itsfaces: the outer face 82 and the inner face 81.

The ring 9 thus comprises:

-   a cylindrical base 91 which covers or crowns the peripheral edge 83    of the second frame 8,-   a first side flap 92 which at least partially covers a peripheral    portion of the inner face 81 of the second frame 8 and a peripheral    portion of the outer face 72 of the first frame 7, and-   a second side flap 93 which covers a portion of the outer face 82 of    the second frame 8.

The first side flap 92 has a general S shape forming a shoulder pressingagainst the inner face 81 of the second frame 8.

This first side flap 92 comprises, from the base 91, firstly a firstportion 92 a which covers a portion of the inner face 81 of the secondframe 8, an elbow 92 b, a second portion 92 c which extendssubstantially in parallel to the axis Y1 while moving away from theinner face 81, and a third portion 92 d which extends transverselytowards the axis Y1 from an end of the second portion, until itlaterally reaches the outer face 72 of the first frame 7.

Because of this form, the first side flap 92 and the second side flap 93crimp the ring 9 onto the extension 85 of the second frame 8. The ring 9is solidly attached to this second frame 8, and the second and thirdportions 92 c, 92 d of the first side flap are shaped to maintain atleast some clearance in the direction of the axis Y1 so that the firstframe 7 can rotate relative to the second frame 8.

In one embodiment of the invention, presented in FIGS. 3 to 5, the ring9 comprises:

-   a cylindrical base 91 which covers or crowns the two peripheral    edges 73, 83,-   a first side flap 92 which at least partially covers a peripheral    portion of the outer face 72 of the first frame 7, without covering    any portion of the inner face 81 of the second frame 8, said inner    face 81 solely facing the inner face 71 of the first frame 7, and-   a second side flap 93 which covers a portion of the outer face 82 of    the second frame 8.

The base 91 extends substantially in the direction of the axis Y1directly between the first side flap 92 and the second side flap 93.This ring 9 therefore encloses the first and second frames 7, 8 of thehinge mechanism.

The ring 9 of the invention therefore differs from the ring of the priorart by its first side flap 92 which does not include any contact withone of the inner faces of the frames. In particular, the ring 9 has nocontact with the inner face 81 of the second frame 8. In other words,the ring 9 does not press on one of the inner faces 71, 81. For example,it does not press on a portion of the inner face 81 of the second frame8.

The ring 9 is therefore an annular piece having an axis Y1 and having aC-shaped cross-section with its opening facing the axis. The base 91which extends along the direction of the axis Y1 corresponds to thevertical portion of the C shape. The first and second side flaps 92, 93correspond to the horizontal arms of the C shape.

The first and second flaps 92, 93 are formed by folding or bending aring preform, towards the first and second frames 7, 8. A first foldingor bending reshapes the preform to shape the first flap 92 towards thefirst frame 7. A second folding or bending reshapes the resultingpreform to shape the second flap 93 towards the second frame 8, thissecond folding being performed without crimping the frames to each otherand therefore without attaching them to one another.

Axial play in the direction of the axis Y1 is preserved so that thefirst frame 7 can rotate relative to the second frame 8, specificallydue to the method for creating said ring 9 which will be explained belowin the description.

Because of this axial play, the ring 9 encloses the frames 7, 8 withoutcrimping them together. The frames remain able to rotate relative to oneanother about the axis Y1.

The ring 9 is, for example, in contact with a peripheral edge 83 of thesecond frame. Advantageously, it is forcibly pressed onto saidperipheral edge 83. Thus the ring 9 is solidly attached to the secondframe 8.

The ring 9 comprises a slightly conical inner face at the base 91 whichgrips the peripheral edge 83 of the second frame 8 and leaves theperipheral edge 73 of the first frame 7 free. Specifically, the innerface of the ring narrows towards the axis Y1, from the first frame 7 tothe second frame 8. The ring 9 is thus solidly attached to the secondframe 8 while having radial play with the first frame 7 so that thefirst frame 7 can rotate.

Said inner face of the base 91, which is conical in shape, forms forexample an angle of less than 5° with the direction of the axis Y1, andpreferably less than 1°.

The peripheral edge 83 of the second frame may possibly comprise teeth86 that project beyond the diameter of said peripheral edge 83. Theseteeth are, for example, low in height, for example less than 0.5 mm andpreferably less than 0.2 mm. These teeth 86 may be distributed along theentire circumference or in angular sections about the axis Y1, asrepresented in FIG. 5 a. These teeth 86 can have various shapes,including teeth of triangular or trapezoid cross-section, and sinewaves, or waves formed of circle sections. These teeth 86 engage withthe ring 9 when the ring 9 is assembled onto the frame 8. The ring 9 isthus even more solidly attached to the second frame 8.

The second frame 8 advantageously has a diameter greater than or equalto the diameter of the first frame 7. The first frame then has radialplay with the inner face of the base 91 of the ring 9, and the firstframe 7 can rotate relative to the ring 9 and to the second frame 8.

The difference between the diameter of the second frame and the diameterof the first frame is, for example, less than 1 mm. The extension 85found in the prior art therefore does not exist. Its radial volume iseliminated. The total outer diameter of the hinge mechanism 6 is lessthan that of the prior art.

The second frame 8 advantageously has a diameter equal to the diameterof the first frame 7. The extension 85 found in the prior art thereforedoes not exist. The total outside diameter of the hinge mechanism 6 iseven lower. The radial volume is thus reduced even further.

Lastly, the first side flap 92 comprises indentations 95 formed by alocal deformation in the direction of the axis Y1. Local deformation isunderstood to mean a cavity, for example a semi-spherical cavity. Theaxial operational clearance in the direction of the axis Y1, necessaryfor the rotation of the first frame 7 relative to the second frame 8,can thus be reduced. The indentations 95 are greater than or equal tothree in number, and are advantageously distributed regularly along thecircumference of the first side flap.

The hinge mechanism 6 is made according to the method defined below, andas represented in FIGS. 6 a to 6 h.

In a first step, an assembly 60 is provided which comprises:

-   first and second frames 7, 8 suitable for being mounting so that    they can rotate relative to one another about an axis, said frames    comprising, in the direction of the axis, inner faces 71, 81    oriented inward and towards one another, and outer faces 72, 82    oriented outward and away from each other, and comprising, in a    direction perpendicular to the axis, circular peripheral edges 73,    83 distanced from the axis Y1, and-   an annular ring 9 comprising a cylindrical base 91 which covers the    peripheral edges of the frames, and a first side flap 92    substantially perpendicular to the base and which covers at least a    portion of the outer face 72 of the first frame 7.

Note for this assembly 60 that the second side flap 93 of the ring 9 isstill not shaped. It comprises, in the axial extension of the base 91and opposite the first side flap 92, material for forming said secondflap 93 by stamping or crimping around the axis.

All known means and all known methods are usable for making the firstand second frames 7, 8 and the preformed ring 9. These parts may inparticular be formed by stamping sheet metal.

In a second step illustrated in FIG. 6 a, the assembly 60 is mounted ina press 100, which comprises:

a press die 101 comprising a first bore hole 102,

a first lower tool 110 (counter-punch) and a first upper tool 111(punch) which are able to move towards each other within the first borehole 102.

The assembly 60 is set down or placed on the first lower tool 110, forexample by simply stacking from bottom to top: the second frame 8, thefirst frame 7, and the ring 9 with its first side flap 92 extendingabove the first frame 7.

The first bore hole 102 comprises, for example, three cylindricalportions that are coaxial around the axis Y1. A first portion 102 aopening onto the upper surface of the die 101 has a first diameter thatis slightly greater than the outside diameter of the ring 9 stacked ontothe assembly 60. A second intermediate portion 102 b has a seconddiameter slightly less than said outside diameter of the ring 9. Thissecond portion 102 b is positioned as the extension of the first portionand lies beneath it, such that a first narrowing 102 d of the bore hole102 between said first and second portions reduces the diameter of thebore hole 102 from the first diameter to the second diameter. For thefirst and second diameters, the term “slightly” is understood to meanhaving a difference in diameter of less than 1 mm compared to thediameter of the ring 9, and preferably less than 0.2 mm. A third portion102 c has a third diameter which is less than the second diameter. It islocated towards the bottom, as the extension of the second portion 102 band beneath it, such that a second narrowing 102 e further reduces thediameter of the bore hole 102, causing it to change from the seconddiameter to the third diameter. The third diameter corresponds, forexample, substantially to an inside diameter of the first and/or secondside flaps 92, 93 of the ring 9 once it is completely shaped. The firstand second narrowing sections 102 d, 102 e are conical in shape forexample, progressively reducing the diameter of the bore hole 102.

The first lower tool 110 is substantially cylindrical in shape, with itsaxis of revolution coaxial to the axis Y1. Its diameter is less than thethird diameter of the bore hole 102, to enable it to move within allportions of the bore hole. It comprises an upper face 112 onto which theouter face 82 of the second frame 8 is placed, this outer face thenbeing oriented downwards.

The first upper tool 111 is substantially cylindrical in shape, with itsaxis of revolution coaxial to the axis Y1. It comprises an annularprotuberance along its edge, projecting downwards towards the assembly60 placed on the first lower tool 110. This protuberance forms ashoulder which delimits a first outer annular surface 113 perpendicularto the axis and a second inner annular surface 114 perpendicular to theaxis, said two surfaces 113, 114 being offset relative to each other bya first distance in the direction of the axis Y1.

In a third step illustrated in FIG. 6 b, the first upper tool 111 hasbeen lowered towards the assembly 60. The first surface 113 faces thefirst side flap 92 of the ring 9, and the second surface 114 comes intocontact with the first frame 7 and presses downwards onto said firstframe 7. The first and second frames 7, 8 are thus maintained in contactwith each other, their inner faces 71, 81 mutually touching, between thefirst upper tool 111 and the first lower tool 110.

The first distance between the surfaces 113, 114 is slightly greaterthan the thickness of the sheet of the first flap 92. This firstdistance is equal to the thickness of the first flap 92 plus anoperating clearance. The ring 9 can then be moved upward by the upwardforce exerted on said ring 9 until the first flap 92 comes into contactwith the first surface 113. An operating clearance is thus formed underthe first flap 92, between it and the outer face 72 of the first frame7.

In a fourth step illustrated in FIG. 6 c, the first lower tool 110 andthe first upper tool 111 are moved together in a downward direction tobring the axial extension of the base 91 into contact with the secondnarrowing 102 d of the first bore hole 102. The ring 9 thus partiallyenters the first narrowing 102 d, and for example a portion of it facingthe peripheral edge 83 of the second frame 8. This first narrowing 102 dlocally reduces the diameter of the ring 9 and radially squeezes orcrimps it onto the peripheral edge 83 of the second frame 8, attachingthem solidly together. In this step, the die 101 exerts an upward forceon the ring 9, due to friction. The ring 9 thus maintains the positiondescribed above during this step, meaning a position in which the firstside flap 92 is in contact with the first surface 113 of the first uppertool 111, which guarantees that the operating clearance between thefirst side flap 92 and the first frame 7 is maintained.

This fourth step allows solidly attaching the ring 9 to the second frame8 by radially crimping it on, with the ring in the correct position formaintaining an axial operating clearance that allows the rotation of thefirst frame 7 relative to the second frame 8.

This fourth step can be carried out in various manners, possiblycombined. In fact, the second frame 8 may comprise the teeth 86, or thering 9 may have a substantially conical base 91, or the outside diameterof the peripheral edge of the second frame 8 may be greater than theinside diameter of the base 91.

In a fifth step illustrated in FIG. 6 d, the first lower tool 110 andthe first upper tool ill are again moved downward, such that the axialextension of the base 91 is forced into the second narrowing 102 e. Thesecond narrowing has a conical shape which clasps or bends the axialextension of the base 91 in order to begin shaping the second side flap93. This second narrowing 102 e forms a first angle with the axis Y1,for example between 30° and 60°. It is preferably substantially equal to45°, or one or two degrees more or less. The partially formed secondflap 93 then is temporarily at an angle corresponding to said firstangle. In this step, the die continues to exert upward force on the ring9, which guarantees the predetermined position. In addition, thispredetermined position cannot vary due to the radial crimping in thefourth step. The bend is therefore shaped on the ring 9, said ring beingin said predetermined position in the direction of the axis Y1. Theoperating clearance in the axial direction is thus guaranteed, and theaxial extension of the ring 9 assumes the form that is angled at thefirst angle for said predetermined position of the ring 9.

The hinge mechanism 6 assembly 60 is then extracted from the press 100by moving the first upper tool 111 and the first lower tool 110 upward,in particular by exerting a first upward force F1 on the first lowertool 110.

This fifth step allows partially bending the second side flap 93 inorder to shape it. It is possible for the method of the invention to dowithout this intermediate step, and directly perform the complete ortotal bending described in the following steps.

In a sixth step illustrated in FIG. 6 e, the hinge mechanism 6 assembly60 is positioned at another location in the press 100. At this location,the press die 101 comprises a second bore hole 104 that is differentfrom the first bore hole 102, and the press 100 comprises a second lowertool 120 and a second upper tool 121 that are able to be moved towardseach other within the second bore hole 104.

The second bore hole 104 is a simple bore hole that is cylindrical inshape, having a single inside diameter that is slightly greater than theoutside diameter of the ring 9. The ring 9 and the assembly 60 can thusslide within this second bore hole 104. The assembly 60 is installed inthis second bore hole 104 on the second lower tool 120; the second sideflap 93, partially formed and angled at the first angle, is then placedagainst an annular surface 122 of the second lower tool 120. Thisannular surface 122 is substantially perpendicular to the axis.

The second upper tool 121 has a shape similar to the first upper tool111. It comprises an annular protuberance extending in the direction ofthe axis Y1. This forms a shoulder delimiting a first outer annularsurface 123 perpendicular to the axis and a second inner annular surface124 perpendicular to the axis. However, these two surfaces 123, 124 areoffset in the direction of the axis Y1 by a second distance which isgreater than the first distance of the first upper tool 111. The firstsurface 123 can no longer come into contact with the first flap 92. Onlythe second surface 124 is able to come into contact with the outer face72 of the first frame 7, in order to push the first frame 7 against thesecond frame 8.

In a seventh step illustrated in FIG. 6 f, the hinge mechanism 6assembly 60 is positioned on the second lower tool 120. Then, the secondupper tool 121 is brought down against the outer face 72 of the firstframe 7, and exerts a downward force on the first frame 7 which pushesthe assembly 60 towards and against the second lower tool 120.

The annular surface 122 of the second lower tool 120 then reshapes thesecond flap 93 bent at the first angle, until it assumes the shape ofthe annular surface 122, meaning until the second flap 93 issubstantially perpendicular to the axis Y1, and until it is in contactwith the outer face 82 of the second frame 8.

Because the second upper tool 121 is pressing against the outer face 72of the first frame 7, and not against the first flap 92 of the ring 9,the operating clearance in the axial direction between the first flap 92and the first frame 7 is maintained during this step of folding thesecond side flap 93 to 90°.

The assembly 60 is thus transformed into a hinge mechanism 6 with a ring9 that is simple in shape, meaning without a radial extension to supportthe usual crimping of the ring 9 in the prior art. In addition, theaxial operating clearance is maintained so that the first frame 7 canmove rotationally relative to the first frame 8.

This seventh step allows completing the bending of the second side flap93.

The two steps, the fifth step of partial bending and seventh step ofcompleted bending, allow progressively folding this second side flap 93,with precise positioning in the direction of the axis which guaranteesthe axial operating clearance for the rotation of the frames relative toeach other.

In an eighth step illustrated in FIG. 6 g, the hinge mechanism 6 isfinally removed from the press 100 by moving the second upper tool 121and the second lower tool 120 upwards, in particular by exerting asecond upward force F2 on the second lower tool 120. FIG. 6 h shows thehinge mechanism 6 completely removed from the second bore hole 104 ofthe press 100.

The indentations 95 in the first side flap 92 can then be made before orafter the formation of the second side flap 93, described in the stepspresented above.

Said steps are only one embodiment of the invention; variations arepossible. The method of the invention allows shaping a more simple ring9 due to the step or steps of the method which allow forming the secondside flap 93 by pressing against the outer face 72 of the first frame 7.The first distance of the first upper tool allows ensuring that an axialoperating clearance is maintained between the frames 7, 8 and the sideflaps 92, 93 of the ring 9.

With this method, the ring 9 does not have any portion that is incontact with one of the inner faces of the frames.

The ring 9 is thus simple in shape, encloses the frames, and allows theframes to rotate relative to each other.

1. A hinge mechanism for a vehicle seat, comprising: first and secondframes mounted so that they can rotate relative to one another about anaxis, said frames comprising inner faces oriented inward and facing oneanother, outer faces oriented outward and away from each other, andcircular peripheral edges distanced from the axis, and an annular ringcomprising a base which covers the peripheral edges of the frames, andfirst and second side flaps which cover at least a portion of each ofthe outer faces, wherein the base has a cylindrical shape which extendsin the direction of the axis directly between the first side flap andthe second side flap, and the ring does not comprise a portion incontact with one of the inner faces of the frames.
 2. The hingemechanism according to claim 1, wherein axial play along the directionof the axis is preserved between the first side flap and the first frameduring the formation of the second side flap against the second frame.3. The hinge mechanism according to claim 1, wherein the second framehas a diameter greater than a diameter of the first frame, and thedifference between said diameters is less than 1 mm.
 4. The hingemechanism according to claim 1, wherein the second frame has a diameterequal to a diameter of the first frame.
 5. The hinge mechanism accordingto claim 1 4, wherein the peripheral edge of the second frame is inclose contact with an inner face of the base (91) in order to attach thering solidly to the second frame.
 6. The hinge mechanism according toclaim 1, wherein the peripheral edge of the second frame comprises teethwhich engage with the inner face of the base in order to attach the ringsolidly to the second frame.
 7. The hinge mechanism according to claim1, wherein the first side flap comprises indentations extending fromsaid first flap in the direction of the outer face of the first frame,said indentations being greater than or equal to three in number.
 8. Thehinge mechanism according to claim 1, wherein the base of the ring (9)comprises a conical inner face in order to grip the peripheral edge ofthe second frame radially and leave the peripheral edge of the firstframe free to rotate.
 9. A seat of a vehicle, comprising first andsecond parts connected to each other by a hinge mechanism according toany of the above claims, the first frame being attached to the firstpart and the second frame being attached to the second part.
 10. Theseat according to claim 9, wherein the first part is a frame of a seatback and the second part is a frame of a seat bottom.
 11. A method formaking a hinge mechanism for a vehicle seat, comprising the followingsteps: a) an assembly is provided which comprises: first and secondframes able to be mounted so that they can rotate relative to oneanother about an axis, said frames comprising inner faces orientedinward and towards one another, outer faces oriented outward and awayfrom each other, and circular peripheral edges distanced from the axis,and an annular ring comprising a cylindrical base which covers theperipheral edges of the frames, and a first side flap which covers atleast a portion of the outer face of the first frame, b) a second sideflap is formed by folding a portion of the ring towards the outer faceof the second frame and by pressing against the outer face of the firstframe.
 12. The method according to claim 11, wherein the following stepis carried out between steps a) and b): the ring is positioned relativeto the first frame with a predetermined clearance with a first toolcomprising first and second surfaces, the first surface being adapted topress against the first side flap, the second surface being adapted topress against the first outer surface, and said surfaces being offset inthe direction of the axis to ensure said predetermined clearance betweenan inner surface of the first side flap and the first outer surface ofthe first frame, the ring being pushed towards said first tool and saidfirst tool being pushed towards said first frame so that said surfacesare pressing against one another.
 13. The method according to claim 11,wherein the ring is squeezed radially inward onto the peripheral edge ofthe second frame.
 14. The method according to claim 11, wherein step b)is carried out in at least the two following sub-steps: b1) the portionof the ring is folded to a first angle to form a flange sloping at saidfirst angle, and b2) said flange is folded to a second angle,substantially 90°, to form the second side flap facing the outer face ofthe second frame, the assembly being pushed towards a die by a firsttool pressing against the outer face of the first frame.
 15. The methodaccording to claim 14, wherein the first angle is between 30° and 60°,and preferably substantially equal to 45°.